Electrophoresis has been widely used for several decades as a method for separating ionized compounds. More recently, there has been growing interest in capillary electrophoresis (CE) as a general, high-efficiency means of separating complex mixtures. In CE, the separation is carried out in a capillary tube with a typical inner diameter of 5 to 100 .mu.m and a total length of 30 to 100 cm. The small radial dimensions of the capillary allow Joule heat to be dissipated efficiently, which in turn allows potentials as high as 30 kV to be applied across the length of the capillary. As a result, excellent separation efficiencies (&gt;1,000,000 theoretical plates) have been reported for many compounds, often in analysis times as short as a few minutes When compared with chromatographic separation procedures, CE can offer a significant improvement in both speed and efficiency for the separation of charged species.
With a typical CE instrument, separation of a mixture usually requires between 5 and 30 minutes. Although this time is fast relative to many competitive procedures, it is slow relative to many chemical events. Another problem is that the traditional methods of sample introduction (e.g., electromigration and hydrostatic pressure) are relatively slow and unwieldy. As a result, CE has not been used as a method for monitoring dynamic chemical systems. To gain this capability, it is necessary to increase the speed of the analysis. One method for achieving this goal is to reduce the time required for the electrophoretic separation. This cannot be achieved by simply increasing the potential across the capillary (and maintaining the same capillary length) or by decreasing the length of the capillary (and maintaining the same potential). Increasing the potential leads to excessive Joule heating and decreasing the length of the capillary without increasing the field strength adversely affects resolution.
It is an object of the present invention to provide an improved device and method for increasing the speed of electrophoretic and chromatographic separations. It is another object to provide an improved capillary system wherein an electric field can be concentrated in a particular section of a capillary column. It is a further object to provide a high-frequency sample modulation device that can be employed for multiplex chromatographic and electrophoretic separations.